Field
The present disclosure relates to an instrument for use with a polyaxial bone anchoring device and to a system including the instrument and a polyaxial bone anchoring device. The polyaxial bone anchoring device includes a receiving part for receiving a rod and for accommodating a head of a bone anchoring element. The head can be clamped by exerting a pressure onto it via a clamping element. The instrument includes a first member and a second member displaceable relative to the first member. The first member is configured to engage the receiving part in a positive-fit manner and the second member is configured to engage the clamping element to adjust the clamping force applied onto the head.
Description of the Related Art
A variety of tools for use with polyaxial bone anchors are known. US 2011/0004222 A1 describes a tool having a tubular counter-holding portion configured to engage a receiving part of a bone anchor, and a driven shaft extending through the counter-holding portion. The driven shaft is configured to engage a locking element of the bone anchor, for example a set screw. The locking element is tightened using the driven shaft while the receiving part is held with the counter-holding portion.
U.S. Pat. No. 8,926,671 describes a receiving part for receiving a rod and for coupling the rod to a bone anchoring element. The receiving part includes a receiving part body for accommodating a head of the bone anchoring element and a pressure element with a flexible portion to clamp an inserted head. The pressure element is movable along a longitudinal axis of the receiving part body from an insertion position where the head is insertable into the receiving part body to a pre-locking position where the head is clamped in the receiving part body by a pre-stress exerted by the pressure element. The pressure element is further movable to a locking position where the head is locked in the receiving part body. The pre-stress exerted by the pressure element allows a desired angular position of the bone anchoring element to be maintained relative to the receiving part by friction before the head of the bone anchoring element is finally locked.